An existing motor (an electric device) typically comprises a rotational position sensor disposed on an axial end portion of a shaft of a motor section for detecting a rotational position of the motor section and a circuit substrate disposed outside of the end portion of the shaft on the axial line and having one or more electronic components mounted thereon. In such motor apparatus, detecting accuracy of the rotational position sensor is decreased or a life-span thereof is shortened if heat generated from electronic components is conducted to the rotational position sensor. Accordingly, how to release the heat generated from electronic components to the outside has long been the issue. Japanese Patent Application Publication No. 1992-67758 (JP H04-67758A) discloses a circuit substrate having electronic components mounted thereon is received in a plate-like casing; a metal plate is disposed between the bottom wall of the casing and the circuit substrate; and a synthetic resin is filled into the casing to cover entirely the electronic components. In this manner, heat generated from electronic components is released through the metal plate and the casing. Japanese Patent Application Publication No. 1988-45900 (JP S63-45900A) discloses a heat conductive member having flexibility is connected both to electronic components and a radiation plate so that heat generated from the electronic components may directly be released to the outside via the radiation plate.